Radio telescope Effelsberg turns 50

The 100-metre antenna has written scientific history and is still one of the top telescopes today

May 06, 2021

The 100-metre antenna of the Max Planck Institute for Radio Astronomy is celebrating its 50th birthday. After three years of construction, its official opening was celebrated on 12 May 1971. The telescope is located in an Eifel valley about 40 kilometres southwest of Bonn, not far from the villages of Effelsberg and Lethert. Over the past five decades, the "Effelsberg Radio Dish" has been continuously upgraded and is still one of the most powerful telescopes on Earth.

The picture shows the 100 m radio telescope Effelsberg a little before its opening in May 1971. The first scientific observation ("First Light") already took place on April 23, 1971.

Since its beginnings in the 1930s, radio astronomy has become an important method for exploring the universe, because it penetrates into depths of the universe that remain blocked to visible light. For example, the discovery of new celestial bodies such as quasars and pulsars, as well as distant galaxies, can be attributed to this branch of astronomy. At least four Nobel Prizes in physics have been awarded for radio astronomical results. Custom-built telescopes are used to observe radio waves. In Germany, the 100m radio telescope of the Max Planck Institute for Radio Astronomy (MPIfR) is by far the largest of its kind - 50 years after its completion, it is still the largest fully steerable radio telescope in Europe and the second largest on Earth.

The list of scientific and technical milestones is long, from the first discovery of the molecules water and ammonia outside the boundaries of our Milky Way in 1977/79 to a world record in angular resolution of only 11 microarcseconds (equivalent to the diameter of a 1-cent coin on the surface of the Moon) by Space VLBI observations including the 100-m telescope. It also features technical milestones such as the installation of a new subreflector with active-surface elements in 2006 and the commissioning of a second radio telescope on site, the Effelsberg station of the European LOFAR telescope network.   

The historical photograph shows the 100 m radio telescope shortly before its opening in 1971. In this picture it can be seen very nicely that the lower elements of the supporting structure do not appear in white, but rather dark. In fact, this part of the telescope was initially painted in blue. However, the resulting bad temperature behaviour very quickly led to re-painting this part of the telescope in white as well. Painting is still a regular part of the annual maintenance work at the Effelsberg telescope. The painters come every summer for about eight weeks in July/August. Then painting work takes place during the day, while at night the telescope is still available for an astronomical measurement program.

The first 1318 days in 17280 pictures. A construction film from 1971

The Effelsberg radio telescope

The first 1318 days in 17280 pictures. A construction film from 1971

Currently, the observing program with the 100-m radio telescope Effelsberg is dominated, as usual in this time of the year, by observations within international networks (Very Long Baseline Interferometry, VLBI), in which the 100-m radio telescope is connected with other radio telescopes on Earth in order to form virtual radio telescopes across continents and oceans to achieve the highest angular resolution. The Effelsberg radio telescope is in demand for this kind of observations because of its large collecting area.  

With a diameter of 100 metres, the Effelsberg radio telescope, inaugurated on 12 May 1971, is one of the two largest fully mobile radio telescopes on Earth.

Flight over the 100-metre Effelsberg radio telescope

With a diameter of 100 metres, the Effelsberg radio telescope, inaugurated on 12 May 1971, is one of the two largest fully mobile radio telescopes on Earth.

The Effelsberg radio telescope also played a role in the investigation of the central region of the galaxy M87 (M87*) At the heart of this Milky Way system, some 55 million light years away, lurks a gigantic black hole. Its shadow has become one of the most famous images in astronomy, published on 10 April 2019.Another focus of the observing program for the 100-m radio telescope is on pulsars and fast radio bursts (FRBs). These observations require very high time resolution in the range of microseconds.  

"Even after 50 years, our radio telescope is a top-class astronomical instrument.  Over the past decades, apart from the basic structure, almost all components have been constantly renewed and improved. The demand for observing time remains high, and observation requests come from scientists all over the world," says Dr. Alex Kraus, station manager of the Effelsberg Radio Observatory. Effelsberg has repeatedly shown its versatility in the past. The ability to keep using new, specially developed cutting-edge technology for the receiver systems will keep the Effelsberg radio telescope at the top of the world for the foreseeable future," concludes Professor Michael Kramer, director at the MPIfR and responsible for the radio observatory with the 100-m telescope.



As a retrospective of 50 years of research work so far, a new hiking trail, the Time Travel Trail, is being opened around the telescope these days, describing a series of special events from these five decades at a total of 20 stations - from the opening of the radio telescope in 1971 to this year's anniversary



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